Currently most factory produced vehicles have their axle assemblies mounted on coil springs, leaf springs, or air suspension assemblies with roll bars and shock absorbers. These vehicles rely on the rigidity of these parts to eliminate unwanted side to side swaying of the vehicle due to the wind, uneven road surfaces or passing vehicles. In many cases, the overall allowable dimensional clearances between the suspension parts along with the flexing of the spring assemblies, air suspension components, roll bars, and shock absorbers won't keep the vehicle from experiencing notable unwanted side to side swaying. This swaying occurs when the vehicle frame is allowed to move from side to side independent of the axle assembly. In other words, the frame moves from side to side and the axle assembly does not. In many vehicles, especially motor homes, school buses, extended vans, older and/or high-mileage vehicles, the swaying can be extreme enough to produce an unsafe driving condition. This swaying action requires immediate steering corrections by the driver to keep the vehicle going straight down the road; in extreme situations, it requires continuous corrections.
Prior art devices provide a single sway bar design to attempt to correct this condition. An example of this design is shown in FIG. 7. The sway bar assembly has rotational bearing type mounting attachments on each end. The sway bar assembly is attached perpendicular to the vehicle frame by a frame attachment bracket on one end and crosses to the opposite side of the vehicle where it is attached to the axle assembly by an axle or spring attachment bracket on the other end. Published Application No. US 2002/0005623 A1 item 88, U.S. Pat. No. 6,523,842 B2 item 88, or U.S. Pat. No. 5,039,124 item 62 are examples of this design. Unwanted side to side movements are then reduced by the addition of the solid connected sway bar device between the frame and axle assembly. A primary problem with this design, even though it reduces side to side swaying during some driving conditions, is that it actually induces side to side frame to axle movement when the vehicle hits a bump or dip in the road and the axle attachment point rebounds up or down. The side to side frame shifting is caused by the arc curve induced by the single sway bar when it moves up and down. The axle attachment point of the sway bar assembly will rotate in an arc curve around the frame attachment point. This design will force the axle assembly to move away from or toward the frame attachment point as the bar travels up or down on a rotational arc. A graphic example of this movement is shown in FIG. 8. On a typical installation, the side induced movement can be approximately three thirty seconds of an inch on an axle that rebounds from its normal riding position up to its maximum allowable height at the frame-mounted axle stop pad. That dimension is approximately one half of the total measured side to side movement of a non sway bar modified stock suspension.
The prior art device actually induces into the vehicle what it is intended to correct. It only works to effectively eliminate side sway when rough roads, wind, or passing vehicles are not affecting the vehicle springs up or down. Simply put, it works as designed when the vehicle is traveling down a smooth highway. During severe driving conditions, however, especially on rough roads, and compounded by passing of large vehicles and extreme crosswinds, vehicle drivers experience the most difficult driving challenges. The best vehicle stability possible is needed at that time and the current single sway bar control system fails to meet that requirement. Instead of correcting the problem, it actually induces side to side shifting when the vehicle is experiencing its greatest stability challenges. An improved sway bar design is needed to correct this disadvantage. Improved vehicle safety and operational control of the vehicle is obtainable with the present invention. The present invention greatly reduces the frame side to side movement in relation to the axle while making sure the axle is allowed to freely move up and down perpendicular to the ground without inducing unwanted side movement.